In order to respond to the need for higher recording density of a magnetic disk device, it has been more necessary to reduce a flying height of a magnetic head slider (simply referred to it as a slider) in recent years. Meanwhile, the smaller a flying height of a slider, R/W (Read/Write) elements are more prone to collide with small protrusions, which are resulted from a rough surface of a magnetic disk. In recent years, a slider has had a small flying height of 30 nm or less relative to a magnetic disk, so that the probability of collision has increased between small protrusions on a surface of a magnetic disk and a magnetic head element (simply referred to it as a head element). In the case of a magnetoresistance effect type head, when a head element collides with small protrusions, the element generates heat and an abnormal signal appears due to thermal asperity (hereinafter, abbreviated as TA). Further, in general, a protective film made of carbon or the like is provided on a surface of a head element to prevent damage such as corrosion. When the protective film on the surface of the head element wears due to collision with small protrusions on a surface of the magnetic disk, the head element cannot be protected and damage such as corrosion is more likely to occur, resulting in shorter lifetime of the magnetic disk device.
JP-A-10-269527 specification discloses means for avoiding collision between small protrusions on a magnetic disk and an element so as to prevent an abnormal signal caused by thermal asperity (TA) on a magnetoresistance effect type head. The means can avoid collision by making a step such that a magnetic head element structure has a recessed part relative to a front slider in.
When a magnetic signal is recorded and reproduced, since current is applied to a magnetic head element, the head element generates heat and a temperature rises. Moreover, due to heat generated on a spindle motor or the like, a temperature rises entirely on a magnetic disk device. The temperature may increase to 60° C. On the other hand, in the head element part, the magnetic head element is generally formed by a nickel alloy and a cobalt alloy, and an insulating film is made of a ceramic such as alumina. The nickel alloy and the cobalt alloy are larger in thermal expansion coefficient than the ceramics of the insulating film. When a temperature rises, the element has a larger amount of thermal expansion than the ceramics of the insulating film. Thus, the element protrudes in a thickness direction of the slider, that is, in a direction of a disk surface.
Hereinafter, as one example a protruding amount of the element will be calculated. It is assumed that a material of the element is a Ni—Fe alloy and a linear thermal expansion coefficient δl/l is set at 1.45×10−5/K. The element is 0.05 mm in length in a thickness direction of the slider. The insulating film is made of alumina and has a linear thermal expansion coefficient δl/l of 7.5×10−6/K. Here, when it is assumed that a temperature increase is 20K and the element and alumina are expanded independently, a protruding amount δl of the element is 7 nm (=7.0×10−6/K×20×0.05×106).
According to the technique disclosed in JP-A10-269527 specification, in the case of a small step between the head element part and the front slider part, when a temperature rises largely, due to protrusion of the element that is caused by thermal expansion, for example, when the slider flies, the element part is disposed at the lowest floating point (the closest point to the disk surface). Hence, the element is more likely to collide with the small protrusions on the surface of the magnetic disk, resulting in an abnormal signal due to damage on the element and thermal asperity.
Moreover, in the case of a large step between the head element part and the front slider part, or in the case of use in the environment at low temperature (e.g., around 0° C.), a distance (magnetic spacing) between the head element and a magnetic medium is increased when the slider flies, resulting in inability to perform recording and reading.
An object of the present invention is in a magnetic head slider and a magnetic disk device using the same, to provide a magnetic disk device or a magnetic head slider which can prevent collision between a head element and small protrusions on a surface of a magnetic disk and can reduce damage and thermal asperity on the head element even when a temperature rises. Further, another object is to provide a magnetic disk device which can perform normal recording and reproducing in response to changes in ambient temperature such as a temperature in a magnetic disk device and an outside air temperature.